The field of sterilization of heat-sensitive three-dimensional objects continues to be the subject of much research. Traditionally, this sterilization is done by impregnating the objects being treated with fluids such as peracetic acid, glutaraldehyde, or hydrogen peroxide or by thermal treatments (dry or moist heat).
Plasma sterilization is emerging as a novel alternative to conventional sterilization techniques. Plasma sterilization offers promising features in terms of efficiency and reliability for inactivating micro-organisms. In addition, this technique can be made to operate at low temperatures (<50° C.), does not require venting time and is safe for the operators, patients and materials. The understanding of plasma sterilization is advancing rapidly, raising high scientific and commercial interests in the development of various types of plasma sterilizers. Nevertheless, no sterilizer making use of the plasma biocide species has yet been brought to the market place. Various reasons can be put forward to explain such a delay: 1) The level of damage induced on the various types of surfaces exposed to such a plasma treatment is an essential issue that has not yet been thoroughly assessed. In particular, as many medical devices (MDs) comprise polymers, the etching of polymers by such a process must be very small, allowing for many re-sterilization cycles. An alternative solution which would permit to avoid substantially degrading or damaging the MDs would be highly desirable. Moreover, variations in the hydrophobicity and biocompatibility of the processed surfaces (intended for limited or extended time of contact with tissues or body fluids) must be scrutinized. 2) Plasma sterilization of MDs must meet the requirements of hospital standards. In that respect, it is customary to sterilize MDs already enclosed in wrapping materials that protect them afterwards from external contamination during transportation and through storage time. However, the various wrapping materials presently used for that purpose are not compatible with a plasma afterglow sterilization process. This is because they strongly absorb UV radiation and also reduce the diffusion toward the MDs of the various plasma particles, namely atoms (e.g. oxygen radicals) and molecules (already present or newly formed), species that are eventually excited (becoming potential UV photon emitters) or ionised. An alternative solution which would permit the inactivation or sterilization of an object located inside a dielectric package would be highly desirable. 3) All parts of a MD should be exposed to substantially the same density or flux of the plasma species, which requires uniformity of the plasma biocide species everywhere in the sterilizer. As an example, consider the case of a plasma sterilizer filled with a large number of MDs: shadowing effects caused by an MD on a nearby other MD are possible, as well as local depletion of the active species (loading effect resulting, for instance, from surface recombination of the plasma species).
Several systems making use of the post-discharge of a plasma have recently been proposed. International application WO2004/050128 describes a method of plasma sterilization of objects of basically dielectric nature and containing a hollow part. In this document, the contaminated objects, and possibly also their packaging, are subjected alternately to the post-discharge of a plasma and to an electromagnetic field of sufficient intensity to create a plasma inside the hollow parts.